1. Field of the Invention
The present invention relates to an apparatus for controlling an automobile air-conditioner having an externally controllable variable displacement compressor.
2. Description of the Related Art
In automobile air-conditioner controllers, when the temperature in a vehicle passenger compartment is high and hence a rapid cooling is needed, various control functions are abandoned to perform a rapid cool-down operation for a predetermined period of time. Japanese Patent Publication No. 1-56922 discloses a displacement control apparatus for controlling the displacement of a variable displacement compressor based on the detected evaporator temperature and the target evaporator temperature. In this apparatus, when a rapid cool-down of the vehicle compartment temperature is desired, the target evaporator temperature is shifted from a normal target evaporator temperature setting value (first target evaporator temperature setting value) to a second target evaporator temperature setting value which is lower than the first evaporator target temperature setting value. Subsequently, when a predetermined condition is satisfied, a third target evaporator temperature setting value which varies progressively from the second toward the first target evaporator temperature setting value is set.
With this arrangement, when a rapid cool-down of the vehicle compartment temperature is needed after a long parking in the sun, for instance, the evaporator target temperature setting value is lowered from the first evaporator target temperature setting value to the second evaporator target temperature setting value to promote or accelerate the cooling effect. Thereafter, when a predetermined condition is reached (for example, after an elapse of a preset time period), the third evaporator target temperature setting value is set. The third evaporator target temperature setting value changes to progressively approach the first evaporator target temperature setting value whereby the vehicle compartment temperature can be regulated to the desired temperature smoothly.
In addition, there have recently been developed variable displacement compressors of the externally controllable type. One example of such compressors is disclosed in Japanese Laid-open Patent Publication No. 2-31918. The disclosed variable displacement compressor is of the swash plate type (also known as the wobble plate type) having a swash plate pivotally mounted on a drive shaft within a crank chamber and pivotally movable about a hinge ball mounted on the drive shaft. The swash plate is pivotally connected with a plurality of pistons movable back-and-fourth within corresponding cylinder bores in response to oscillation of the swash plate. A pressure control valve disposed in confrontation to the crank chamber operates to reduce the quantity of a working fluid flowing from the crank chamber back to an intake side depending on the magnitude of an electric current (I.sub.SOL) supplied to the pressure control valve. As the current intensity or strength (I.sub.SOL) is increased, the pressure in the crank chamber rises to reduce the angle of oscillation of the swash plate and thereby to lower the displacement of the compressor. On the contrary, with a reduction of the current strength, the pressure in the crank chamber goes down, so that the angle of oscillation of the swash plate is enlarged to increase the displacement of the compressor. The current strength (I.sub.SOL) serving as a compressor displacement control signal is determined by the target post-evaporator temperature T'.sub.E and the post-evaporator temperature T.sub.E such that .vertline.T.sub.E -T'.sub.E .vertline.&lt;1 is satisfied.
In the case of the automobile air-conditioner having such a variable displacement compressor, when a need for the rapid cool-down operation arises, the target post-evaporator temperature T'.sub.E is lowered to -10.degree. C., for example, and subsequently the thus lowered target post-evaporator temperature is maintained for a predetermined time period. In this instance, if the vehicle compartment temperature is relatively high at the initial stage of the cool-down operation, the post-evaporator temperature T.sub.E is also high and the current strength (I.sub.SOL) is low on the contrary, so that the compressor is operated at a maximum displacement level. However, from the middle to the final stage of the rapid cool-down operation, the vehicle compartment temperature gradually goes down in response to which the current strength (I.sub.SOL) is increased progressively to lower the displacement of the compressor and to thereby reduce the air quantity. As a consequence, a cooling power supplied to the vehicle passenger compartment goes down and the desired rapid cool-down of the vehicle passenger compartment cannot be accomplished.